Nodejs MQTT：取消订阅不是一个函数

Question

我很好地实施了 MQTT，但我遇到了方法问题unsubscribe。mqttCon.publish() , mqttCon.subscribe(), mqttCon.on()...除此以外，所有其他功能 ( ) 都运行良好。我已经检查了拼写，甚至完成了ctrl +click它，它把我带到了库实现，这意味着它是正确的方法并且引用得很好，但我一直收到下面的错误。我该如何解决？

这是一行： mqttCon.unsubscribe(topic)

TypeError: mqttCon.unsubscribe is not a function

    at noopHandler (/home/dev/project-dir/src/mqtt/processMessage.js:5:13)

    at module.exports (/home/dev/project-dir/src/mqtt/processMessage.js:10:20)

    at MqttClient.client.on (/home/dev/project-dir/src/mqtt/mqttCon.js:16:13)

    at MqttClient.emit (events.js:189:13)

    at MqttClient._handlePublish (/home/dev/project-dir/node_modules/mqtt/lib/client.js:1271:12)

    at MqttClient._handlePacket (/home/dev/project-dir/node_modules/mqtt/lib/client.js:410:12)

    at work (/home/dev/project-dir/node_modules/mqtt/lib/client.js:321:12)

    at Writable.writable._write (/home/dev/project-dir/node_modules/mqtt/lib/client.js:335:5)

    at doWrite (/home/dev/project-dir/node_modules/mqtt/node_modules/readable-stream/lib/_stream_writable.js:428:64)

    at writeOrBuffer (/home/dev/project-dir/node_modules/mqtt/node_modules/readable-stream/lib/_stream_writable.js:417:5)

注意：我使用的是 ES6(Emacscript 6+) javascript 而不是Typescript。节点12.18.1和 npm6.14.6

这是我的连接代码mqttCon.js：

const mqtt = require('mqtt')

const processMessage = require('./processMessage')

const logger = require('../logConf')

const options = {

    host: '',

    port: '',

    username:'',

    password: '',

    protocol: ''

};

const client = mqtt.connect(options)

client.on("connect", function () {

    console.log("MQTT connected  with status: " + client.connected);

    if (client.connected) {

        client.on('message', (topic, message) => {

            processMessage(topic, String(message))

        })

    }

})

Answer 1

你的 mqttCon.js 文件没有client.prototype.unsubscribe = function() {}，所以错误是正确的。您正在定义client为一个模块，但您确实需要mqtt.unsubscribe()在某个地方调用。因此，您需要unsubscribe()向常量添加一个函数client（在这种情况下实际上应该是一个函数var），或者mqtt.unsubscribe()在您的 processMessage.js 文件中需要 mqtt 模块后调用该函数....我认为这与您正在尝试的相反无论如何要做。更新：以上影响了我的想法，问题是我正在导入processMessage.js哪个mqttCon.js又导入了哪个。循环导入，意思是mqttCon(mqttClient) was always not yet initialized inside processMessage.js. 解决方案是当客户端已经初始化并导出为如下模块时，我processMessage.js在块内导入：client.on('connect'....)...client.on("connect", () => {    console.log("MQTT connected  with status: " + client.connected);    if (client.connected) {        client.on('message', (topic, message) => {            require('./processMessage')(topic, String(message))        })    }})